1. Field of the Invention
The present invention relates to a PC Card providing the interface required to connect and use a personal computer or other data processing device to an Integrated Services Digital Network (ISDN) using digital communication lines.
2. Description of the Prior Art
PC Card type modems used with analog communication lines have become capable of increasingly faster transmission rates. Cards manufactured to current ITU-T (CCITT) Recommendations are capable of achieving a maximum 14.4 Kbps under the V.32bis protocol, 28.8 Kbps under V.34, and 33.6 Kbps under V.34bis. Some modems are also capable of simultaneous voice and data communication using a single telephone line by implementing the DSVD (Digital Simultaneous Voice and Data) or VOICE VIEW (registered trademark) modem protocols for simultaneous communication.
At the same time, however, increasing business and residential use of computers, and particularly the rapid spread of Internet access and use, have made even faster transmission of information, images, and audio essential. Applications such as television-conferencing in which data is transmitted by means of data communication protocols while teleconference participants simultaneously talk over a telephone connected to the same transmissions line to describe and discuss the transmitted data also necessitate communication means enabling simultaneous communication.
Communication means capable of both increasing the transmission rate and enabling simultaneous communication are currently available in the form of digital communication means connecting to an Integrated Services Digital Network (ISDN) rather than to conventional analog telephone lines.
The ISDN was designed and developed to efficiently transmit digitized signals from telephones, facsimile machines (faxes), personal computers, and other data sources at a high speed. More specifically, ISDN connections provide two so-called "B channels" each with a 64-Kbps transmission capacity and one "D channel" with a 16-Kbps transmission capacity. A single ISDN line connection provides the same communication capacity as two conventional analog lines. Using this ISDN connection, data can be transmitted at a sustained rate of either 64 Kbps or 128 Kbps by using one or both B channels, and a telephone conversation can be carried on while connected, for example, to the Internet or other network, or facsimiles can be sent and received during a personal computer data communication session.
One means of connecting and using a personal computer or other data processing device with an ISDN connection is an ISDN-interface PC Card conforming to the PCMCIA/JEIDA PC Card standard, hereinafter referred to as an ISDN card.
FIG. 4 is a simplified block diagram of a conventional ISDN card marketed, for example, by BUG Inc. under the brand name LINKBOY.TM. D64K. As shown in FIG. 4 the ISDN card 50 comprises a device connector 52 providing an interface conforming to the PCMCIA/JEIDA PC Card standard for connecting the ISDN card 50 to a personal computer or other data processing device 51; an interface circuit block 53 conforming to the PC Card standard; a controller 54 enabling the various ISDN card functions; memory 55 for storing firmware; S-point interface circuit 56, the interface circuit for the ISDN S-point providing the interface between the controller 54 and the external device connected to the ISDN card 50; an insulating I/O transformer 57; and a line connector 58 for connecting the ISDN digital service unit (DSU). Note that one of the connectors from the connector cable linking the ISDN card 50 with the DSU is connected to the line connector 58.
In this ISDN card 50 the device connector 52 is connected to the controller 54 through the interface circuit block 53. The controller 54 is connected to the memory 55 and to the S-point interface circuit 56. The S-point interface circuit 56 is connected through the I/O transformer 57 to the line connector 58.
Thus configured, the controller 54 operates in response to the send and receive commands input from the data processing device 51 through the device connector 52 and interface circuit block 53 based on the firmware stored to the memory 55 to implement high speed digital communication between the data processing device 51 and the ISDN connection at the 64 Kbps or 128 Kbps transmission rate enabled by ISDN.
Such conventional ISDN cards 50 are, however, designed for data communication using an ISDN connection. As a result, achieving simultaneous voice and data communication with this ISDN card 50 requires access to two communication lines, a digital ISDN line used by the ISDN card, and an analog line to which a telephone may be connected for talking.